Companion planting is getting more and more attention these days. Some may refer to companion planting as selecting the right color combination of ornamentals or using large plants to partially shade smaller plants.

These are good things to consider, but I am referring to planting combinations of plants that reduce damage from pests to both ornamentals and vegetables. Companion planting is obviously appealing to organic gardeners because it is a chemical free way to control pests. It should also appeal to other gardeners who can save time and money by reducing the application of pesticides.

It is not surprising that most insects are attracted to or repelled by the smell of certain plants. Many plants produce scents as a defense mechanism against harmful pests. Therefore, it stands to reason that if we can camouflage certain smells to confuse and repel pests we can protect surrounding plants.

Marigolds, nasturtiums and many herbs, including thyme, mint and basil put out a smell that repels many harmful pests. Marigolds have such a strong scent they are good companions for almost any plant. Plants in the mint family also have biting juices that repel insects. They repel beetles, nematodes and even some animal pests.

In addition to smell, plants produce chemicals that help fend off insects and diseases. The roots of marigolds contain a substance that is toxic to some nematodes. Nematodes are microscopic roundworms that inhabit soil and can damage many types of plants. Interplanting marigolds in the home garden or between row crops will eliminate most nematodes.

Some plants also trap insects. Once trapped they cannot move and feed, resulting in death. Nasturtiums, eggplant and radish are examples of trapping plants.

Let’s not forget that there are many garden helpers such as preying mantises, wasps, ladybugs and spiders that prey on harmful garden pests. Some plants that attract these helpers are carrots, dill, parsnips and parsley. These plants produce small clusters of flowers with strong fragrances, making them good choices for companion plants.

This may start to sound confusing so let’s get down to listing some beneficial combinations.

Dill and basil planted with tomatoes protect the tomatoes from hornworms. Lima beans and cabbage are also known to be good companions for tomatoes.

Tomatoes planted among asparagus may repel asparagus beetles. Tomatoes also repel diamondback moth larvae, which chew large holes in cabbage leaves.

Marigolds, mint and thyme are known to repel cabbage moths.

Chives repel aphids and therefore are good companions for roses. Parsley repels rose beetles. Tomatoes may help to protect roses from blackspot.

Chives repel rust flies in carrots.

Nasturtiums grown near squash may repel squash bugs.

Radishes are a trap plant for cucumber beetles and are good companions for squash and cucumbers.

Sweet alyssum attracts beneficial wasps and is a good companion for bushy crops like potatoes.

Dwarf zinnias attract ladybugs and other predators that protect cauliflower.

There is not much scientific evidence relating to companion planting but most of these combinations have been known to be successful. You can try combinations of your own, however, there are a few combinations you should avoid. White garlic and onions repel many pests and are good companions for most plants but can stunt the growth of beans and peas. Potatoes and beans grow poorly alongside sunflowers. Tomatoes do not thrive when planted near peppers or potatoes. Have fun experimenting and pass your success stories along to your fellow gardeners.

 

Karen O’Neal is an Adams County Master Gardener.